Not Applicable
Not Applicable.
The present invention relates to air preconditioning modules used in combination with HVAC systems and, in particular, relates to a method and apparatus for determining the efficiency of an air preconditioning module.
Historically, commercial buildings were constructed so as to receive large amounts of air from the ambient environment to enable a continuous supply of fresh air into the building. However, during the energy crisis of the 1970""s, buildings were constructed to be more airtight to conserve energy costs associated with heating and cooling large amounts of air. For instance, many HVAC systems only processed a small percentage of outdoor air (e.g. 15%), with the majority of air being re-circulated. This caused germs to permeate throughout the building, causing widespread illness, and resulting in what is now known as xe2x80x9csick building syndrome.xe2x80x9d
In an effort to prevent future sick buildings, heating, ventilating and air-conditioning (HVAC) standards were enacted by the industry""s trade organization, the American Society of Heating Refrigeration and Air-Conditioning Engineers (ASHRAE). In particular, ASHRAE standards increased the amount of outdoor air recommended for commercial type buildings to ensure that adequate amounts of fresh air were supplied to commercial buildings. Prior to the development of reliable air preconditioning modules, the industry had been reluctant to comply with these standards due to the costs associated with conditioning large amounts of outdoor air.
Conventional air preconditioning modules are disposed between the inlet to the outdoor air and the building""s HVAC system. In operation, they receive the outdoor air that is to be supplied to the building, and also receive return air that has been circulated throughout the building, and that is to be exhausted into the outdoor environment. The modules typically include an energy recovery wheel that transfers energy between the exhaust air and the supply air, thereby achieving the goals of 1) reducing costs associated with conditioning the supply air that is circulated within the building, while 2) ensuring that enough fresh air is circulated to prevent sick building syndrome. Because air preconditioning modules are valuable to the user only insofar as they increase the efficiency of the HVAC system, it is desirable to enable the end user to quantify the cost savings of installing such modules.
Traditional methods of determining the efficiency of air preconditioning modules included installing thermocouples (to measure dry and wet-bulb) in the supply inlet, supply outlet and exhaust inlet of the module. The outputs from these modules could be manually read or fed into a PLC to calculate the efficiency of the energy wheel. On a 75% efficient (total, sensible and latent) wheel, this method can determine sensible efficiencies within xc2x17% of the actual value, latent efficiencies within xc2x114% and total efficiencies within xc2x18% during extreme operating conditions such as 95xc2x0 F. dry-bulb/78xc2x0 F. wet-bulb supply inlet air and 75xc2x0 F. dry-bulb/63xc2x0 F. wet-bulb exhaust inlet air. At typical operating conditions such as 82xc2x0 F. dry-bulb/69xc2x0 F. wet-bulb supply inlet air and 75xc2x0 F. dry-bulb/63xc2x0 F. wet-bulb exhaust inlet air, the sensible efficiencies can be determined within xc2x119%, the latent efficiencies within xc2x135% and the total efficiencies within xc2x121% of the actual value.
All of the above examples assume the user is using standard dry-bulb and wet-bulb temperature sensing means with xc2x11xc2x0 F. accuracy in their measurements. In addition to being inaccurate, such a method is labor intensive, and may not provide the user with real-time efficiency information.
The present invention provides a method and apparatus for measuring the efficiency of an air preconditioning module. More particularly, the method includes (a) feeding a supply air stream and return air stream through the matrix, (b) measuring a pressure differential across the matrix in the supply air stream or return air stream, and (c) producing an efficiency value for the matrix based on a pre-established relationship between the measured pressure differential across the matrix and the efficiency of the matrix.
In one aspect, the efficiency may be provided based on the pressure differential of only one of the supply air stream and return air stream when the streams are substantially balanced. In another aspect, the efficiency may be provided based on the pressure differential of both the supply air stream and return air stream when the two streams are unbalanced.
The foregoing and other aspects of the invention will appear from the following description. In the description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, and not limitation, a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must therefore be made to the claims herein for interpreting the scope of the invention.